<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body ng-app="myApp">
    <div ng-controller="mycontroller">
        <input type="text" ng-model="a">+
        <input type="text" ng-model="b">
        <input type="button" value="=" ng-click="bg()">
        <input type="text" ng-model="c">
    </div>

    <script src="angular/angular.js"></script>
    <script>

        var myApp = angular.module('myApp',[]);

        myApp.controller('mycontroller',function($scope){
                $scope.a = '';
                $scope.b = ''; 
                $scope.bg=function(){
                    $scope.c = parseInt($scope.a)+parseInt($scope.b);
                }
        })
    </script>
</body>
</html>